JPH04293018A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To decrease the parasitic capacity generated between a picture element electrode and a data electrode, and a gate electrode and also reduce the generation of crosstalk and a halftone display error by making the corner parts of the picture element round, specially, circular. CONSTITUTION:The liquid crystal display device is formed in sandwich structure wherein two substrates which each have an electrode and an orienting film formed of a high polymer film of polyimide thereupon are combined, and one substrate is provided with the picture element electrode 3, data electrode, and gate electrode 2 as electrodes. The picture element electrode 3 is formed in a nearly rectangular shape having four corners made round and the picture element electrode 3 is formed circularly. Thus, the corner parts of the picture element electrode 3 are made round, specially, circular, so the corner parts of the picture element 3 are reduced in parasitic capacity, the parasitic capacity between the picture element electrode 3 and data electrode 1, and gate electrode 2 is reduced, and the generation of the crosstalk, half-tone display error, etc., is reducible.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a liquid crystal display device.
The present invention relates to a shape of a pixel electrode that can reduce parasitic capacitance occurring between a pixel electrode, a data electrode, and a gate electrode.

0002

[Prior Art] The structure of a conventional general liquid crystal display device is as follows:
As shown in FIG. 2, it has a sandwich structure in which two substrates 5 are combined, each having an electrode 6 and an alignment film 7 made of a polymer film such as polyimide formed thereon. On the other hand, the substrate 5 is provided with a pixel electrode, a data electrode, and a gate electrode as electrodes 6. As shown in FIG. 2, the two substrates 5 are kept at a constant distance by a spacer 9 and bonded together by a sealant 10. Liquid crystal 8 is injected into the space thus created. Further, on each of the substrates 5, polarizing plates 4 are pasted.

[0003] To drive the liquid crystal display device, a voltage is applied to the two substrates 5. The voltage changes the long axis direction of the molecules of the liquid crystal 8, causing the molecules of the liquid crystal 8 to rotate the incident light selected by the polarizing plate 4. In other words, two boards 5
By changing the effective voltage value of the voltage, the intensity of transmitted light or reflected light can be changed.

The current mainstream driving method for liquid crystal display devices is active matrix driving (Lech
ner et al. , IEEE Int. soli
d. st. cir. Conf. of tech p
ap. , pp52-53, feb. 1969). This uses transistors and diodes as switches for pixel electrodes. An active matrix driven liquid crystal element in which the transistor 11 is used as a switch for the pixel electrode 3 will be described below with reference to FIG.

The overall structure is the same as the liquid crystal element shown in FIG. 2, but the difference is that each of the pixel electrodes 3 provided on one of the two substrates 5 This is because a transistor 11 is provided.

[0006] The active matrix driving method described above is such that a voltage can be applied from the data electrode 1 to the pixel electrode 3 only while a pulse is being applied to the gate electrode 2. When a voltage is applied to the pixel electrode 3, charges are accumulated in the liquid crystal 8 located between the pixel electrode 3 and the electrode (counter electrode) of the other substrate 5. Thereafter, no charge is applied to the gate electrode 2 for a certain period of time, but during that period, the liquid crystal itself maintains its display state using the charge accumulated in the liquid crystal 8 itself or the charge accumulated in the liquid crystal and the additional capacitance.

[0007] This method has a feature that the effective value of the voltage applied to the liquid crystal can be sufficiently obtained and the display performance is good because there is little influence from surrounding electrodes.

However, recently there has been a demand for higher definition liquid crystal display devices. (Flat Panel Display '91, Nikkei BP). For this reason, the distance between the pixel electrode 3 and the surrounding data electrodes 1 and gate electrodes 2 becomes narrower, so that the influence of the surrounding data electrodes 1 and gate electrodes 2 appears. That is, parasitic capacitance occurring between the pixel electrode 3, data electrode 1, and gate electrode 2 has become a problem. As the parasitic capacitance increases, crosstalk and halftone display errors occur, resulting in poor display quality (W
．． E. Howard, et al. , conf. r
ec. of the IDRC, p230-235, 1
988. /R. L. Wisnieff, Proco.
f the Conf. Eurodisplay, p
59-62, 1987. /R. L. Wisnieff,
SSDM'90SENDAI, p983-986, 1
990) arises.

The present inventors clarified the cause of the above problem through the following experiment. FIG. 4 shows the results of simulating the pixel capacitance of a liquid crystal display device equipped with conventionally shaped transistors. The size of the pixel electrode 3 is 130
×130 μm, and the distance between the pixel electrode 3, data electrode 1, and gate electrode 2 is 10 μm. The height of the peak in the figure indicates the relative capacitance value. In the case of the conventional shape, the parasitic capacitance between the gate electrode 2 and the pixel electrode 3 is 5.5 fF.
The parasitic capacitance between the data electrode 1 and the pixel electrode 3 was 2.0 fF. The parasitic capacitance value between the gate electrode 2 and the pixel electrode 3 is larger. What should be noted here is that the parasitic capacitance is concentrated around the pixel electrode 3, particularly at the corner portions of the pixel electrode 3.

0010

SUMMARY OF THE INVENTION An object of the present invention is to reduce the parasitic capacitance that occurs between the pixel electrode 3, the data electrode 1, and the gate electrode 2, which was a problem in the prior art. This is to reduce the occurrence of crosstalk, halftone display errors, etc.

[0011]

[Means for Solving the Problems] In the liquid crystal display device of the present invention, the above-mentioned problems have been solved by forming the pixel electrodes into shapes with rounded corners, particularly circular shapes.

0012

[Operation] By making the pixel electrode rounded, particularly circular, it is possible to reduce the parasitic capacitance that has conventionally been concentrated at the corners of the pixel electrode.

[0013]

Embodiment Embodiment 1 FIG. 1(a) shows the main part of a liquid crystal display device of this embodiment. In this liquid crystal display device, the pixel electrode 3 has a substantially square shape with rounded corners.

By rounding the corners of the pixel electrode 3 in this way, the parasitic capacitance that had conventionally accumulated at the corners of the pixel electrode 3, indicated by the two-dot chain line in FIG. 1(a), is significantly reduced. Furthermore, the parasitic capacitance between the gate electrode 2 and the pixel electrode 3 is 5.0 fF, and the parasitic capacitance between the data electrode 1 and the gate electrode 2 is 5.0 fF.
The parasitic capacitance between the pixel electrode 3 and the pixel electrode 3 was 1.7 fF, and the parasitic capacitances at both locations were lower than in the past.

In the liquid crystal display device of this embodiment, since the pixel electrode 3 has rounded corners, the pixel electrode 3
The parasitic capacitance at the corners of the pixel electrode 3 and the data electrode 1 and the gate electrode 2 are reduced. Therefore, according to the liquid crystal display device of this embodiment, occurrences of crosstalk, halftone display errors, etc. can be further reduced.

(Embodiment 2) FIG. 1(b) shows the main part of a liquid crystal display device of this embodiment. The pixel electrode 3 of this liquid crystal display device is formed in a circular shape.

When the pixel electrode 3 is formed into a circular shape in this manner, the parasitic capacitance not only at the corners but also at the periphery is significantly reduced, as shown by the two-dot chain line in FIG. 1(b). The parasitic capacitance between the gate electrode 2 and the pixel electrode 3 was 1.8 fF, and the parasitic capacitance between the data electrode 1 and the pixel electrode 3 was 1.2 fF. These values are smaller compared to Example 1. In other words, this shows that by making the pixel electrode 3 circular, the parasitic capacitance around the pixel electrode 3 is reduced.

In the liquid crystal display device of this embodiment, since the pixel electrode 3 is circular, the parasitic capacitance at the corner portions of the pixel electrode 3 can be significantly reduced. Therefore, according to the liquid crystal display device of this embodiment, crosstalk and halftone display errors can be further reduced.

[0019]

[Effects of the Invention] As explained above, in the liquid crystal display device of the present invention, the pixel electrode has a rounded corner, particularly a circular shape, so that the parasitic capacitance generated between the pixel electrode, the data electrode, and the gate electrode is reduced. You can do less. Therefore, according to the liquid crystal display device of the present invention, occurrences of crosstalk, halftone display errors, etc. are further reduced.

[0020]

[Brief explanation of drawings]

FIG. 1 (a) is a perspective view showing the shape of a pixel electrode of a liquid crystal display device of Example 1. (b) A perspective view showing the shape of a pixel electrode of the liquid crystal display device of Example 2.

FIG. 2 is a schematic diagram showing the structure of a general liquid crystal display device.

FIG. 3 is a perspective view showing a liquid crystal display device using thin film transistors as active elements.

FIG. 4 is a schematic diagram showing the results of simulating capacitance using a conventional pixel electrode shape.

[Explanation of symbols]

1 Data electrode 2 Gate electrode 3 Pixel electrode 4 Polarizing plate 5 Glass substrate 6 Electrode 7 Alignment film 8. Liquid crystal 9 Spacer 10 Adhesive 11 Transistor

Claims (2)

[Claims] 1. A liquid crystal display device characterized in that a pixel electrode has a shape with rounded corners. 2. A liquid crystal display device characterized in that a pixel electrode has a circular shape.